1. Field of the Invention
The present invention is directed to an automated method and apparatus for detecting and removing contaminant particles from a moving pulp mat in a paper making process.
2. Background of Related Art
In paper making processes, it is important to remove as many contaminants as possible from the pulp used to make the final paper products. Contaminants, such as metal, plastic, rubber or wood particles, which are not removed from the pulp will usually be chopped into smaller pieces in the subsequent refining processes. These smaller pieces eventually surface as prominent impurities in finished paper. Paper products having such impurities or imperfections are generally considered to be of inferior grade and in some instances the paper is rendered unsalable.
Contaminant removal has heretofore been performed generally as a manual operation. Human operators are stationed at an appropriate location adjacent the pulp processing equipment, typically at some point between the digesting and refining equipment, where the pulp is travelling in a wet mat form. The operators visually inspect the moving mat and manually pick the contaminant particles off of the mat surface as the mat travels past their inspection station.
The manual operation has several disadvantages which result in less than satisfactory removal. Particles embedded in the mat will generally pass by the inspection station undetected. Some smaller surface contaminants are also likely to pass by undetected, partially due to the size (about 6 feet in width) and travel speed (125 feet per minute) of the mat. Operator fatigue and inability to maintain concentration over a typical eight-hour shift further detract from the effectiveness of this method of contaminant removal. These factors combine to produce a larger than desirable quantity of contaminant particles entering the pulp mat refining equipment.
Various devices are known in the art for sensing defects, such as dirt or other inclusions, in a moving sheet of material. Some of these devices use a light sensing means to detect differences between normal, defect-free sections and sections containing defects. One such known apparatus further provides a means for marking the travelling sheet where the defect is detected, but generally none of the known devices provide further means for removing the defect from the travelling sheet.
Another device known in the art uses spray nozzles to create slits in a travelling paper mat to prevent the propagation of breaks detected in the paper mat, the breaks being detected by photocells. No provision is made in this apparatus for automatic removal of contaminant particles.
It is therefore an object of the present invention to provide an apparatus which is capable of automatically detecting the presence of contaminants in a pulp mat and automatically removing the contaminants detected from the pulp mat as the mat travels to a refining station, thereby obviating the need for manual inspection and removal stations.
It is a further object of the present invention to provide an apparatus capable of detecting contaminants disposed in the interior of the pulp mat in addition to detecting those on the surface.
It is a further object of the present invention to provide a pulp mat cutting means operatively coupled with a contaminant detecting means wherein a portion of the pulp mat containing the defect may be removed from the mat without stopping the travel of the mat.
Yet another object of the present invention is to provide a plurality of jet spray nozzles for cutting rectangular sections containing defects from the moving pulp mat and a catch trough for receiving and disposing of the sections cut from the pulp mat.
A further object of the present invention is to provide a method for detecting contaminants present in a moving pulp mat and for removing the detected contaminants using water spray cutters controlled by detection information.